Retaining wall and landscaping works, geocomposite supplied and installed, quantity 1,000 SQM

For a medium-scale retaining wall and landscaping project in Rewari, Ocean Non Wovens supplied and installed 1,000 square metres of geocomposite drain behind the wall face. The geocomposite filters and drains water from the backfill, which allowed a slimmer drainage zone, removed the need for a thick stone chimney drain and protects the wall from water pressure during the monsoon.

Project background and challenges

The site needed a retaining structure to stabilise a landscaped slope next to a newly built access path. There were three constraints: limited access for heavy plant, the client’s wish for a clean landscaped finish, and monsoon rain that saturates the soil and can build up hydrostatic pressure behind the wall. A conventional coarse-aggregate chimney drain with large drainage pipes would have meant more excavation and imported stone, adding cost and time.

The drainage solution had to:

1. Prevent hydrostatic pressure building up behind the wall.
2. Minimise excavation and imported aggregate.
3. Leave a clean, plantable landscaped finish.

Why a geocomposite drain

A drainage geocomposite combines a high-flow core with a non woven geotextile filter bonded to it. The filter lets pore water through and holds back soil particles; the core carries the water down to the base drain. A sheet a few millimetres thick can do the job of a granular chimney drain that would otherwise be several hundred millimetres wide.

• Drainage: Water moves quickly to the collection points, lowering the water pressure on the wall. This matters most where there is little space behind the wall.
• Filtration: The geotextile facing keeps fines out of the core, so the drain keeps its flow capacity over time.
• Less stone, simpler construction: The geocomposite replaces layers of stone or gravel, which cuts material volume, truck movements and handling on a constrained site.

Design inputs and specification

Ocean Non Wovens worked with the client and the design engineer on material and installation specifications. The design inputs were:

• Wall height and facing type (low-to-medium height, modular facing).
• Backfill type and gradation. Coarser backfill drains better, but the site fill was variable, so choosing the right filter was critical.
• Expected rainfall intensity and seasonal groundwater behaviour, which set the flow the drain had to carry.

Material specification (summary):

• Product: Geocomposite sheet drain, non woven filter bonded to a high-flow core.
• Flow capacity: Matched to the estimated peak seepage, carrying water to the base drain. In-plane flow is measured as transmissivity under ASTM D4716, at a normal load representing the backfill pressure.
• Filtration: Non woven geotextile with an apparent opening size (AOS, ASTM D4751) chosen from the local soil gradation to limit clogging.
• Durability: Polymer and thickness chosen to survive construction and remain chemically and biologically stable in the ground.

Installation on site

1. Site preparation: Excavated to design depth, removed unsuitable organic material and compacted the bearing areas.
2. Base drain: A shallow trench at the wall toe with perforated pipe, surrounded by aggregate where required. The geocomposite was tied into this collection system so the flow path is continuous.
3. Geocomposite placement: Rolls were cut to suit the wall panels and fixed vertically behind the wall face, filter side towards the soil. Overlaps and end laps followed the supplier’s guidance, and critical vertical seams were sealed or firmly overlapped so water could not bypass the core.
4. Backfilling: Free-draining backfill was placed in layers without damaging the composite. Heavy point loads directly on the exposed core were not allowed.
5. Outlets and testing: Outlets and collection points were checked with controlled water flow tests during installation to confirm drainage was unobstructed.
6. Landscaping: After the structural work, topsoil and planting were reinstated, with the geocomposite concealed behind the wall.

Geocomposite cores can be punctured during construction, so the crew was briefed to keep sharp tools away and a sacrificial geotextile was used where the risk of mechanical damage was higher.

Performance in the first year

• No signs of saturation at the rear face during monsoon events that caused visible ponding elsewhere on site.
• No blockages at outlets during scheduled inspections.
• Less excavation and no thick stone chimney drain. Ocean Non Wovens estimates this cut imported aggregate for the drainage component by approximately 60–70% compared with a stone-drain design of equivalent capacity.

Lessons from the field

1. Detailing decides performance. Even a high-capacity geocomposite fails if outlet connections are constricted or overlaps are too short. Extra time went into the junction details on this job.
2. Survivability before nominal capacity. Construction damage is common. Protective layers and installer training prevent most of it.
3. Inspect the outlets. Geocomposites avoid the clogged stone drains and failed weep holes of older designs, but they are hidden. Outlets still need periodic inspection.
4. Plan for roots. Roots can grow into the filter layer. The right geotextile AOS, and a root barrier where needed, protect the long-term flow.
5. Buy on performance, not unit price. Cheaper geocomposites may have thinner cores or poorer filters. Ask suppliers for index test data (flow capacity, AOS, tensile strength and puncture resistance) to check against the design.

The same principle scales up to large industrial sites. Ocean supplied 2,000 sq m of drainage geocomposite to the BCGCL Project at Jharsuguda, Odisha, India’s first coal-to-ammonium nitrate plant.

For the numbers behind a drain like this one, see our guide on how a geocomposite drainage layer is sized, which covers transmissivity, reduction factors and which Ocean grade suits a retaining wall.

Recommendations for engineers and clients

• Match the filter AOS to the gradation of the retained soil rather than using a generic value.
• Protect the exposed core during backfilling with sacrificial geotextile or plywood where plant will operate close by.
• Detail outlets and connections for easy inspection. A small access chamber at the outlet saves trouble later.
• Consider geocomposites where access is restricted or where reducing truck movements and imported stone is a project goal.

On the Rewari project, Ocean Non Wovens supplied 1,000 SQM of geocomposite selected for the site’s soil conditions, helped with detailing, supervised installation and checked drainage performance during commissioning. For a retaining wall, slope or landscaped earth-retaining structure, contact Ocean Non Wovens for a project review and quotation based on your site conditions.